Various molding processes such as resin transfer molding (RTM) processes involve loading dry reinforcement layers into a mold, closing the mold, injecting a thermosetting resin composition into the mold and curing the resin via the application of heat. One of the bottlenecks in such a process is loading the reinforcement into the mold. The individual layers of fabrics must be cut and shaped to conform to the various curvatures in the mold. This can be very time consuming, especially for layups (preforms) involving foam cores. It would be desirable to assemble the reinforcement outside of the mold and load only that structure (or preform) into the mold at one time.
Two common approaches in assembling the preform are (1) to tie layers together with reinforcement strands or (2) to use a viscous liquid or solid resin as an adhesive to hold the layers together. Either method is unsatisfactory from the standpoint of ease or economy of operation.
Tying the layers together is economically unsound since the labor costs associated with this method are too high. Gluing the layers together with a resin is a better approach but resins systems such as Spray 77 available from 3M Corporation which are currently employed adversely affect the mechanical properties of subsequent molded composites at elevated temperatures in the presence of moisture. The solid resins have been previously applied by solvent techniques which are energy intensive, and affect fiber sizing. The liquid resins have been applied using messy painting techniques and require solvent recovery systems.
It would be desirable to have available a method for assembling preforms for molding processes which did not involve tying, gluing or solvent recovery.
The present invention provides a method for preparing preforms for use in molding processes which avoids the use of tying, gluing or solvent recovery.